Battery management for patient support apparatuses

ABSTRACT

A patient support apparatus, such as a bed, recliner, cot, stretcher, operating table, or the like, includes battery-powered circuitry whose functions are reduced, but not eliminated, as the battery charge level falls below a threshold. Electrical power may be cut off to one or more components of the battery-powered circuitry while still providing battery-supplied electrical power to the other components of the circuitry. A user interface provides battery status data, including a replacement status of a rechargeable battery, and allows a user to select different formats for displaying battery status data. Such formats include displays of battery charge level information not only in manners specific to the battery, but also in manners relative to the patient support apparatus, such as displays of how many, or how much of, one or more functions the patient support apparatus is able to perform based on the battery&#39;s current charge level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.16/549,572 filed Aug. 23, 2019, by inventors Aaron Furman et al. andentitled BATTERY MANAGEMENT FOR PATIENT SUPPORT APPARATUSES, which inturn claims priority to U.S. patent application Ser. No. 15/151,523filed May 11, 2016, by inventors Aaron Furman et al. and entitledBATTERY MANAGEMENT FOR PATIENT SUPPORT APPARATUSES, which in turn claimspriority to U.S. provisional patent application Ser. No. 62/160,155filed May 12, 2015 by inventors Aaron Furman et al. and entitled BATTERYMANAGEMENT FOR PATIENT SUPPORT APPARATUSES, the complete disclosures ofall of which are hereby incorporated herein by reference.

BACKGROUND

The present disclosure relates to patient care devices, such as patientthermal temperature management systems, as well as patient supportapparatuses, such as beds, cots, stretchers, recliners, and the like.

Patient care devices often employ one or more batteries that provideelectrical power for carrying out their functions. Often, the user ofthe patient care device is given little information about the state ofthe battery, other than how charged it currently is. Existing patientcare devices may also not take steps to better manage the battery, givenits current charge state and/or its overall health.

SUMMARY

According to some embodiments, the present disclosure relates to patientcare devices that are designed to include one or more of the followingfeatures: provide more efficient usage of the battery, convey betterinformation regarding the state of the battery, facilitate propermaintenance of the battery, and better conserve the battery's power. Insome embodiments, the patient care devices include a sleep state thatcuts off power to all instruction-executing processors in the device,and/or the devices include automatic power conservation steps that aretaken before the battery is drained, and/or the devices includeimprovements in the display of battery status information that betterenable the user to make decisions about using the device while beingpowered by a battery.

According to one embodiment, a patient support apparatus is providedthat includes a frame, wheels, a support surface, an actuator, abattery, and a control system. The support surface is adapted support apatient thereon and the actuator is adapted to move at least a portionof the support surface. The battery powers the actuator. The controlsystem monitors a charge state of the battery, compares the charge stateof the battery to a threshold and, when the charge state is lower thanthe threshold, disables movement of the actuator in a first manner butenables movement of the actuator in a second manner.

In some embodiments, the first manner includes moving the actuator in afirst direction, and the second manner includes moving the actuator in asecond direction opposite to the first direction. Still further, in someof such embodiments, the actuator controls a height of the supportsurface, and the first direction raises a height of the support surfaceand the second direction lowers a height of the support surface.

In other embodiments, the first manner includes moving the supportsurface to a Trendelenburg position and the second manner includesmoving the support surface out of the Trendelenburg position. In stillother embodiments, the first manner includes moving the support surfaceto a reverse Trendelenburg position and the second manner includesmoving the support surface out of the reverse Trendelenburg position. Insuch embodiments, the patient support apparatus may be a bed or astretcher.

In still other embodiments, the first manner includes moving the supportsurface to a first configuration and the second manner includes movingthe support surface away from the first configuration. The firstconfiguration may be an egress configuration adapted to allow thepatient to exit the patient support apparatus more easily than when thepatient support apparatus is in other configurations, while the secondconfiguration is a configuration that does not allow the patient to exitthe patient support apparatus as easily as the first configuration.

In still other embodiments, the patient support apparatus is a reclinerhaving a seat, a backrest, a leg rest, a leg rest actuator, and abackrest actuator. In such embodiments, the control system is furtheradapted to disable movement of the leg rest actuator in a third mannerbut enable movement of the leg rest actuator in a fourth manner when thecharge state is lower than the threshold, and to disable movement of thebackrest actuator in a fifth manner but enable movement of the backrestactuator in a sixth manner when the charge state is lower than thethreshold. The third and fifth manners may include moving the supportsurface to a first configuration and the fourth and sixth manners mayinclude moving the support surface away from the first configuration.

According to another embodiment, a patient support apparatus is providedthat includes a frame, wheels, a support surface, a battery, and acontrol system. The support surface is adapted to support a patientthereon and the battery is adapted to power a component of the patientsupport apparatus. The control system monitors a replacement status ofthe battery, compares the replacement status of the battery to a firstthreshold and to a second threshold, provides an indication to a userthat the battery should be replaced when the replacement status isbetween the first and second thresholds, and stops supplying power tothe component when the replacement status is smaller than the firstthreshold.

In other embodiments, the control system stops supplying power to thecomponent when the replacement status is smaller than the firstthreshold even if the battery still includes sufficient charge to poweran actuator.

In some embodiments, the replacement status of the battery is a numbercalculated from a formula. The formula may take into account an age ofthe battery since installation in the patient support apparatus, acumulative number of times the battery has been re-charged, and/or aratio of a current charge capacity of the battery compared to a previouscharge capacity of the battery (such as the charge capacity when thebattery was initially installed in the patient support apparatus).

In another embodiment, the patient support apparatus includes a secondcomponent and the control system is further adapted to stop supplyingpower to the second component when the replacement status is smallerthan the first threshold and the second component is activated in aparticular manner. The particular manner refers to moving the actuatorin a first direction, but not a second direction opposite to the firstdirection, in at least some embodiments.

According to another embodiment, a patient support apparatus is providedthat includes a frame, wheels, a support surface, a plurality ofcomponents powered by a battery, a display, and a control system. Thecontrol system monitors a current charge state of the battery anddisplays both a first indication and a second indication on the display.The first indication indicates a first relationship of the currentcharge state of the battery to a first set of the plurality ofcomponents and the second indication indicates a second relationship ofthe current charge state of the battery to a second set of thecomponents.

In some embodiments, the first set of components includes a motor fordriving a first one of the wheels and the second set of componentsincludes an actuator for changing a height of the support surface. Thefirst indication may provide an estimated distance the motor can drivethe patient support apparatus based on the current charge state of thebattery. The second indication may provide an estimated number of timesthe height of the support surface can be changed before the batteryshould be recharged.

In some embodiments, the second set is a subset of the first set.

Still further, in some embodiments, the patient support apparatus is acot, the first set of the plurality of components includes an actuatorto lift the support surface from a lowered position to a raisedposition, and the first indication provides an estimated number of liftsthat can be powered by the battery until the battery should berecharged. The second indication may provide an estimated amount of timebefore the battery should be recharged.

In some embodiments, the control system automatically switches betweendisplaying the first indication and displaying the second indicationdepending upon a state of the patient support apparatus. For example, insome embodiments, the patient support apparatus includes a propulsionsystem adapted to be activated by a user, and the control systemautomatically displays the first indication when the propulsion systemis activated and automatically displays the second indication when thepropulsion system is not activated. The first indication may indicate anestimated distance the propulsion system can propel the patient supportapparatus before the battery should be recharged, and the secondindication may provide an estimated amount of time before the batteryshould be recharged.

According to another embodiment, a patient support apparatus is providedthat includes a frame, wheels, a support surface, a battery, a display,a control system, and a user interface. The control system monitors acurrent charge state of the battery and the user interface allows a userto select between displaying first or second indications of the chargestate of the battery on the display.

In some embodiments, the first indication provides an estimate of acapacity of the battery and the second indication provides an estimatedpercentage of a remaining life of the battery before the battery shouldbe replaced. The estimated percentage is based at least partially upon acumulative number of discharge cycles experienced by the battery, insome embodiments.

In other embodiments, the first indication provides an estimate of anumber of motion cycles of the support surface, or an estimate of timeuntil the battery runs out. When providing an estimate of time, the timeestimate may be based upon a current rate of usage of the battery andmay change if the current rate of usage of the battery changes. In someembodiments, the control system maintains a history of the estimate oftime and displays at least a portion of the history of the estimate oftime.

In still other embodiments, the first indication provides an indicationof when the battery should be replaced, such as an estimated percentageof a remaining life of the battery until it should be replaced.

The patient support apparatus may be a cot having an actuator adapted tolift the support surface from a lowered position to a raised position,wherein the first indication provides an estimated number of lifts thatcan be powered by the battery until the battery should be recharged.Alternatively, the patient support apparatus may include a propulsionsystem wherein the first indication indicates an estimated distance thepropulsion system can propel the patient support apparatus before thebattery should be recharged. In such embodiments, the first indicationmay include a map of at least a portion of a healthcare facility,wherein the map is marked to graphically identify which locations liewithin the estimated distance.

The display displays a speed of the patient support apparatus, in someembodiments.

The second indication may indicate a level of power currently beingdelivered by the battery to the patient support apparatus.

In still other embodiments, the patient support apparatus includes anexit detection system adapted to detect, when activated, if the patientis about to exit the support surface, and the first indication providesan estimate amount of time the exit detection system can remainactivated before the battery should be recharged.

The control system is adapted, in some embodiments, to change thepatient support apparatus from an awake state to a sleep state when thecontrol system detects inactivity for more than a threshold amount oftime, the sleep state consuming less power than the awake state. In thesleep state, the control system shuts off electrical power to allmicrocontrollers on the patient support apparatus. Circuitry is providedto awaken the patient support apparatus from the sleep state, and thecircuitry is implemented completely in hardware and utilizes nosoftware.

A voltage monitor is included in some embodiments that is adapted tomonitor a voltage of the battery both when the patient support apparatusis in the sleep state and when the patient support apparatus is in theawake state. The voltage monitor shuts off power to all electricalcomponents of the patient support apparatus when the voltage monitordetects that a voltage of the battery has fallen below a voltagethreshold and the patient support apparatus is not plugged into anelectrical power outlet. The voltage monitor turns on power to at leastsome of the electrical components of the patient support apparatus onlywhen the patient support apparatus receives electrical power having avoltage greater than the voltage threshold.

According to still another embodiment, a patient support apparatus isprovided that includes a frame, wheels, a support surface, a battery, adisplay, a control system, and an interface. The control system monitorsa current charge state of the battery. The interface includes aplurality of relays in electrical communication with a connector thatare adapted to receive a nurse call cable. The control system changes astate of one or more of the relays when the control system detects thatthe charge state of the battery has fallen below a threshold, therebyproviding an indication to a conventional nurse call system that thebattery of the patient support apparatus has fallen below the threshold.

The patient support apparatus may also include includes an exitdetection system wherein the control system changes the state of thesame relay, or a different relay, when the exit detection system detectsthat the patient is about to exit the support surface. The controlsystem may also change the state of yet another relay when the controlsystem detects that the charge state of the battery has fallen below asecond threshold that is lower than the threshold. In some embodiments,the controller retains the relay in the changed state even whenelectrical power is no longer supplied to the control system.

According to still another embodiment, a patient support apparatus isprovided that includes a frame, wheels, a support surface, an actuator,a battery, and a control system. The control system includes amicrocontroller for controlling the actuator and a voltage monitor formonitoring a voltage level of the battery. The control system terminatespower to the microcontroller if the voltage level of the battery dropsbelow a threshold and allows power to flow to the microcontroller if thevoltage level of the battery is above the threshold.

The patient support apparatus may also include a user interface whereinthe control system terminates power to the user interface if the voltagelevel of the battery drops below the threshold. In some embodiments, thecontrol system further includes a sleep circuit adapted to change thepatient support apparatus from an awake state to a sleep state if thecontrol system detects inactivity for more than a threshold amount oftime. The sleep state consumes less power than the awake state. Thecontrol system terminates power to the microcontroller while the patientsupport apparatus is in the sleep state, and supplies power to themicrocontroller while the patient support apparatus is in the awakestate provided the voltage level of the battery exceeds the threshold.Circuitry adapted to awaken the patient support apparatus from the sleepstate to the awake state is also included, and in some embodiments thiscircuitry is implemented completely in hardware and utilizes nosoftware.

The control system, in some embodiments, shuts off power to allelectrical components of the patient support apparatus when the voltagemonitor detects that the voltage level of the battery has fallen below asecond threshold lower than the threshold and the patient supportapparatus is not plugged into an electrical power outlet. The controlsystem also turns on power to at least some of the electrical componentsof the patient support apparatus only when the patient support apparatusreceives electrical power having a voltage greater than the threshold.The control system may continue to supply power to a wake circuit whilethe battery is below the threshold but above a second threshold. Thewake circuit resupplies power to the microcontroller when the wakecircuit is activated. In some embodiments, the wake circuit is coupledto a user interface, and the wake circuit is activated when a usertouches the user interface.

In any of the above-described embodiments, the patient support apparatusmay be a recliner having a seat, a backrest, and a leg rest, or it maybe a bed or stretcher having a movable patient support surface.

Before the various embodiments disclosed herein are explained in detail,it is to be understood that the claims are not to be limited to thedetails of operation, to the details of construction, or to thearrangement of the components set forth in the following description orillustrated in the drawings. The embodiments described herein arecapable of being practiced or being carried out in alternative ways notexpressly disclosed herein. Also, it is to be understood that thephraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. Further, enumeration may beused in the description of various embodiments. Unless otherwiseexpressly stated, the use of enumeration should not be construed aslimiting the claims to any specific order or number of components. Norshould the use of enumeration be construed as excluding from the scopeof the claims any additional steps or components that might be combinedwith or into the enumerated steps or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a first patient support apparatusembodying various aspects of the present disclosure;

FIG. 2 is a perspective view of a second patient support apparatusembodying various aspects of the present disclosure;

FIG. 3 is a diagram of a first embodiment of a control system usable onany of the patient support apparatuses described herein, including thoseshown in FIGS. 1 and 2 ;

FIG. 4A is a first portion of a detailed circuit diagram of portions ofthe control system of FIG. 3 ;

FIG. 4B is a second portion of the detailed circuit diagram of FIG. 4A;

FIG. 5 is a second embodiment of a control system usable on any of thepatient support apparatuses described herein;

FIG. 6 is a flowchart of an automatic and/or manually selectable batterydata display algorithm that may be incorporated into any of the patientsupport apparatuses described herein;

FIG. 7A is a first illustrative graphic for displaying battery datausing the display algorithm of FIG. 6 for a patient support apparatusadapted to lift a patient, such as, but not limited to, a cot;

FIG. 7B is a second illustrative graphic for displaying battery datafrom the patient support apparatus of FIG. 7A;

FIG. 7C is a third illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 7A;

FIG. 8A is a first illustrative graphic for displaying battery datausing the display algorithm of FIG. 6 for any of the patient supportapparatuses described herein;

FIG. 8B is a second illustrative graphic for displaying battery datafrom the patient support apparatus of FIG. 8A;

FIG. 8C is a third illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 8A;

FIG. 8D is a fourth illustrative graphic for displaying battery datafrom the patient support apparatus of FIG. 8A;

FIG. 8E is a fifth illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 8A;

FIG. 8F is a sixth illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 8A;

FIG. 9A is a first illustrative graphic for displaying battery datausing the display algorithm of FIG. 6 for a patient support apparatushaving a propulsion system;

FIG. 9B is a second illustrative graphic for displaying battery datafrom the patient support apparatus of FIG. 9A;

FIG. 9C is a third illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 9A;

FIG. 9D is a fourth illustrative graphic for displaying battery datafrom the patient support apparatus of FIG. 9A; and

FIG. 9E is a fifth illustrative graphic for displaying battery data fromthe patient support apparatus of FIG. 9A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A patient support apparatus 20 according to one embodiment of thepresent disclosure is shown in FIG. 1 . Patient support apparatus 20, asshown in FIG. 1 , is implemented as a recliner. It will be understood,however, that patient support apparatus 20 can be alternativelyimplemented as a bed, such as shown in FIG. 2 . In still otherembodiments, patient support apparatus 20 may be implemented as a cot, astretcher, or still other types of apparatuses that are capable ofsupporting a patient. Further, it will be understood that theembodiments of the present disclosure discussed herein can alternativelybe incorporated into other types of patient care devices, such as, butnot limited to, temperature management systems for controlling thetemperature of patients. One such temperature management system isdisclosed in commonly assigned U.S. patent application Ser. No.14/282,383 filed May 20, 2014 by inventors Christopher J. Hopper et al.and entitled THERMAL CONTROL SYSTEM, the complete disclosure of which ishereby incorporated herein by reference.

Patient support apparatus 20 of FIG. 1 includes a support surface orseat 22, a backrest 24, an armrest 26, a plurality of wheels 28, anadjustable leg rest 30, and two touch screens 32 (one positioned oneither side of patient support apparatus 20, with only one visible inFIG. 1 ). Backrest 24 is angularly adjustable with respect to seat 22about a pivot axis that extends perpendicularly out of the plane of thepage of FIG. 1 so that a patient seated on seat 22 can change how far heor she leans back on patient support apparatus 20. Leg rest 30 is alsomovable from a stowed position (shown in FIG. 1 ) to an extendedposition that supports a patient's legs in a substantially horizontalorientation. The movement and physical construction of patient supportapparatus 20 of FIG. 1 may take on any of the forms disclosed incommonly assigned U.S. patent application Ser. No. 14/212,253 filed Mar.14, 2014 by inventors Christopher Hough et al. and entitled MEDICALSUPPORT APPARATUS, the complete disclosure of which is incorporatedherein by reference.

The control of the movement of patient support apparatus 20 is carriedout via the touch screens 32. Touch screen 32 includes a plurality ofbuttons, icons, images, and/or other types of controls that, whenpressed, implement one or more functions associated with patient supportapparatus 20. More specifically, such controls may include controls formoving seat 22, backrest 24, and/or leg rest 30; controls for activatingand deactivating an exit detection system; controls for activating anddeactivating a patient lockout function; and controls for carrying outstill other functions.

A number of indicators may also be provided on touch screen 32 that areselectively illuminated, depending upon the state of patient supportapparatus 20 and/or the state of one or more of the controls. Forexample, touch screen 32 may include one or more icons, images,graphics, or other types of indicia that provide one or more indicationsregarding the current state of a battery on board patient supportapparatus 20. These indicia are discussed in greater detail below,including the number of such indicia that are displayed, the time atwhich the indicia are displayed, and the manual and/or automaticselection that is undertaken to determine which indicia to display.

FIG. 2 illustrates another example of a patient support apparatus 20that may incorporate one or more features of the present disclosure.Patient support apparatus 20 of FIG. 2 is implemented as a bed andincludes a base 34 having a plurality of wheels 28, a pair of lifts 36supported on the base, a litter frame 38 supported on the lifts 36, anda support deck 40 supported on the litter frame 38. Patient supportapparatus 20 of FIG. 2 further includes a headboard 42, a footboard 44,and a plurality of siderails 46. Siderails 46 are all shown in a raisedposition in FIG. 2 but are each individually movable to a lower positionin which ingress into, and egress out of, patient support apparatus 20is not obstructed by the lowered siderails 46.

Footboard 44 includes a first user interface 56 having a touch screen32. Patient support apparatus 20 of FIG. 2 further includes a pluralityof additional user interfaces 56, including first and second caregiveruser interfaces 56 a and 56 b positioned on the outside faces of headend siderails 46, as well as a patient user interface 56 c positioned onthe inside faces of head end siderails 46. Although user interfaces 56a, b, and c are not shown as including a touch screen, it will beunderstood that patient support apparatus 20 of FIG. 2 can be modifiedto include one or more touch screens associated with any one or more ofuser interfaces 56 a, 56 b, and/or 56 c.

Lifts 36 are adapted to raise and lower litter frame 38 with respect tobase 34 Lifts 36 may be hydraulic actuators, electric actuators, or anyother suitable device for raising and lowering litter frame 38 withrespect to base 34. In the illustrated embodiment, lifts 36 are operableindependently so that the tilting of litter frame 38 with respect tobase 34 can also be adjusted. That is, litter frame 38 includes a headend 48 and a foot end 50, each of whose height can be independentlyadjusted by the nearest lift 36. This allows patient support apparatus20 to move to both a Trendelenburg position and a reverse Trendelenburgposition. Patient support apparatus 20 is designed so that when anoccupant lies thereon, his or her head will be positioned adjacent headend 48 and his or her feet will be positioned adjacent foot end 50. Thecontrol of lifts 36 is carried out via one or more of the userinterfaces 56 a, 56 b, and 56 c.

Litter frame 38 provides a structure for supporting support deck 40,headboard 42, footboard 44, and siderails 46. Support deck 40 provides asupport surface for a mattress 52, or other soft cushion, so that aperson may lie and/or sit thereon. The top surface of the mattress orother cushion forms a support surface for the occupant. Support deck 40is made of a plurality of sections, some of which are pivotable aboutgenerally horizontal pivot axes. In the embodiment shown in FIG. 2 ,support deck 40 includes a head section, a seat section, a thighsection, and a foot section. The head section, which is also sometimesreferred to as a Fowler section, is pivotable about a generallyhorizontal pivot axis between a generally horizontal orientation (notshown in FIG. 2 ) and a plurality of raised positions (one of which isshown in FIG. 2 ). The thigh section and foot section may also bepivotable about generally horizontal pivot axes. The pivoting of thevarious sections of deck 40 is controlled via one or more of userinterfaces 56 a, 56 b, and 56 c.

The mechanical construction of patient support apparatus 20 of FIG. 3 isthe same as, or nearly the same as, the mechanical construction of theModel FL27 InTouch® critical care bed manufactured and sold by StrykerCorporation of Kalamazoo, Michigan. This mechanical construction isdescribed in greater detail in the Stryker Maintenance Manual (version2.4; 2131-409-002 Rev. B) for the Model FL27 InTouch® Critical Care Bed,published in 2010 by Stryker Corporation of Kalamazoo, Michigan, thecomplete disclosure of which is incorporated herein by reference. Inother embodiments, the mechanical construction of patient supportapparatus 20, when implemented as a bed, may be the same as, or includeelements of, the Model 3002 S3 bed manufactured and sold by StrykerCorporation of Kalamazoo, Michigan. This mechanical construction isdescribed in greater detail in the Stryker Maintenance Manual(3006-109-002 Rev. D) for the MedSurg Bed, Model 3002 S3, published in2010 by Stryker Corporation of Kalamazoo, Michigan, the completedisclosure of which is also incorporated herein by reference. It will beunderstood by those skilled in the art that patient support apparatus20, when implemented as a bed, can be designed with other types ofmechanical constructions, such as, but not limited to, those describedin commonly assigned, U.S. Pat. No. 7,690,059 issued to Lemire et al.,and entitled HOSPITAL BED; and/or commonly assigned U.S. Pat.publication No. 2007/0163045 filed by Becker et al. and entitled PATIENTHANDLING DEVICE INCLUDING LOCAL STATUS INDICATION, ONE-TOUCH FOWLERANGLE ADJUSTMENT, AND POWER-ON ALARM CONFIGURATION, the completedisclosures of both of which are also hereby incorporated herein byreference. The mechanical construction of patient support apparatus 20may also take on forms different from what is disclosed in theaforementioned references, including, as noted, being implemented asstructures other than beds

Regardless of whether patient support apparatus 20 is implemented as arecliner, a bed, or some other type of patient support structure, FIG. 3illustrates a control system 54 that is usable with the patient supportapparatus 20, whatever its particular physical implementation. Controlsystem 54 includes a main controller 58, a deep discharge circuit 60, awake circuit 62, a sleep power supply 64, one or more sensors 66, andone or more H-bridges 68 for controlling and powering one or moreactuators 70, such as, but not limited to, one or more motors. Controlsystem 54 also includes one or more touch screens 32. In the embodimentshown in FIG. 3 , touch screen 32 includes both a set of touch sensors80 and a display 82. In some embodiments, such as that shown in FIG. 3 ,control system 54 also includes an exit detection system 72.

Exit detection system 72, when armed, is adapted to issue an alert(audio and/or visual; and local and/or remote) when it detects that anoccupant of patient support apparatus 20 may be about to, or alreadyhas, exited from patient support apparatus 20. In some embodiments, exitdetection system 72 may take on any of the forms, and include any of thefeatures, of those exit detection systems described in commonly assignedU.S. Pat. No. 5,276,432 issued to Travis and entitled PATIENT EXITDETECTION MECHANISM FOR HOSPITAL BED; or commonly assigned U.S. patentapplication Ser. No. 14/212,367 filed Mar. 14, 2014 by inventors MichaelJoseph Hayes et al. and entitled PATIENT SUPPORT APPARATUS WITH PATIENTINFORMATION SENSORS; commonly assigned U.S. patent application Ser. No.62/065,242 filed Oct. 17, 2014 by inventors Marko N. Kostic et al. andentitled PERSON SUPPORT APPARATUS WITH MOTION MONITORING; commonlyassigned U.S. patent application Ser. No. 61/989,243 filed May 6, 2014by inventors Marko N. Kostic et al. and entitled PERSON SUPPORTAPPARATUS WITH POSITION MONITORING; or commonly assigned U.S. patentapplication Ser. No. 62/076,005 filed Nov. 6, 2014 by inventors Marko N.Kostic et al. and entitled EXIT DETECTION SYSTEM WITH COMPENSATION, thecomplete disclosure of all of which are incorporated herein byreference.

Power for control system 54 is supplied either by a battery 74 or anon-battery power supply 76. Non-battery power supply 76, in at leastone embodiment, refers to the electrical power supplied by an electricalcord that is coupled to an alternating current (A/C) wall outlet. Inother words, power supply 76 refers to the mains electricity, in atleast one embodiment. Battery 74 may take on any of a variety ofdifferent suitable forms, depending upon the particular implementationof patient support apparatus 20 and the functions that are to be carriedout by control system 54. In some embodiments battery 74 is a lead-acidbattery, while in other embodiments battery 74 is any one of alithium-ion battery, a nickel-cadmium battery, a nickel-metal hydridebattery, a nickel-zinc battery, or still other types of batteries. Inmost embodiments, battery 74 is rechargeable, but this is notnecessarily the case in all embodiments.

Control system 54 (FIG. 3 ) is adapted, in at least one embodiment, toselectively supply power to a set of sleep components 78. Sleepcomponents 78 are components of patient support apparatus 20 that areable to be put to sleep and awakened. That is, in at least oneembodiment, control system 54 selectively puts sleep components 78 intoa sleep state and awakens sleep components 78 into an awake state. Whenoperating in the sleep state, control system 54 stops supplying power tosleep components 78, and when operating in the awake state, controlsystem 54 re-supplies electrical power to sleep components 78. As shownmore clearly in FIG. 3 , sleep components 78 include main controller 58,H-bridge 68, actuator 70, display 82 of touch screen 32, and, ifpresent, sensors 66 and/or exit detection system 72.

The logic for determining whether or not sleep components 78 will be putinto a sleep state or an awake state is carried out by wake circuit 62and controller 58. More specifically, wake circuit 62 determines when tochange sleep components 78 from the sleep state to the awake state, andmain controller 58 determines when to change sleep components 78 fromthe awake state to the sleep state. Because main controller 58 is partof the set of sleep components 78, it will not receive any electricalpower when sleep components 78 are in the sleep state. As a result, maincontroller 58 does not play any role in awakening from the sleep stateto the awake state. Instead, the transitioning into the awake state iscarried out by wake circuit 62 and various other components that are notpart of sleep components 78. As will be discussed in greater detailbelow, the electrical components that are responsible for carrying outthe transition from the sleep state to the awake state are all comprisedof hardware (no instruction executing components). As a result of thisdesign feature, as well as other described below, control system 54consumes substantially no power while in the sleep state, thereby moreeffectively conserving the power within battery 74.

Control system 54 is also designed to prevent battery 74 from beingdeeply discharged. That is, control system 54 is designed to preventbattery 74 from discharging beyond a threshold level. The specific valueof the threshold may vary, depending upon the type of battery 74, thefunctions performed by battery 74, and/or the form in which patientsupport apparatus 20 is implemented. Although other thresholds may beused, in at least one embodiment, control system 54 is adapted toprevent battery 74 from discharging to a state of charge that is lessthan 20% of its full state of charge. Control system 54 does this viadeep discharge circuit 60, as will be discussed in more detail below.When deep discharge circuit 60 determines that the state of charge ofbattery 74 is less than the threshold, it cuts off power to allelectrical components of patient support apparatus 20 (includingitself). When power is shut off in this manner, patient supportapparatus 20 can only regain electrical power by plugging its electricalcord back into a mains electrical supply, or otherwise providingelectrical power via non-battery power supply 76.

A more detailed description of control system 54, including wake circuit62 and deep discharge circuit 60, will now be provided. Wake circuit 62(FIG. 3 ) controls a power switch 84 that, when closed, supplies powervia a power line 90 to sleep components 78, and when open, terminatespower to power line 90 and sleep components 78. Wake circuit 62 thuscontrols whether or not sleep components 78 are in the sleep state orthe awake state via switch 84. Regardless of whether or not wake circuit62 has switched sleep components 78 into a sleep state or an awakestate, wake circuit 62 receives its own electrical power from sleeppower supply 64. As will be explained more below, sleep power supply 64provides electrical power regardless of whether or not sleep components78 are awake or asleep. Sleep power supply 64 only stops supplyingelectrical power when deep discharge circuit 60 shuts off electricalpower to all components (due to battery 74 having drained to itsthreshold, or below).

Wake circuit 62 includes three logic input lines 86. A first logic inputline 86 a comes from touch sensor 80; a second logic input line 86 bcomes from main controller 58, and a third logic input line 86 c comesfrom power supply 76 (or more accurately, a sensor coupled to powersupply 76 that detects the presence of power supply 76). Wake circuit 62functions as a logical OR gate with respect to these three logic inputlines 86 a, b, and c. That is, if any of the inputs lines 86 a, b, or chave a logic HIGH value, then wake circuit 62 will output a logic HIGHvalue that will close switch 84, thereby allowing electrical power toflow to sleep components 78 via power line 90. Only if all of the threelogic input lines 86 a, b, and c have a logic LOW value will wakecircuit 62 open switch 84, thereby cutting off electrical power to allof sleep components 78 and thus putting those components into the sleepstate.

Input line 86 a has a logic HIGH value whenever a user touches touchscreen 32. That is, whenever touch sensors 80 detect that a user hastouched touch screen 32, touch sensor 80 outputs a logic HIGH value oninput line 86 a. Main controller 58 outputs a HIGH value on input line86 b whenever it detects activity at touch screen 32, and continues tooutput a HIGH value on input line 86 b for a threshold amount of timeafter such activity is detected. More specifically, whenever touchsensor 80 detects a users touch, in addition to sending a logic HIGHvalue to wake circuit 62 via input line 86 a, it also send a signal tomain controller 58 via line 88. When main controller 58 receives thissignal, it starts a timer. Main controller 58 continues to output a HIGHvalue to wake circuit 62 via input line 86 b for as long as the timercontinues to run. When the timer expires, controller 58 stops sending aHIGH signal along line 86 b and instead switches line 86 b to a logicLOW signal. Main controller 58 further resets the timer any time touchsensor 80 detects a person touching touch screen 32 (or touching anyother controls that are part of the user interface), so long as thetimer has not yet expired. In at least one embodiment, the timer is setto a value on the order of five minutes, although it will be understoodthat other threshold amounts of time may be used. Whatever its precisevalue, the use of the time threshold by controller 58 ensures that sleepcomponents 78 will remain awake for at least the threshold amount oftime after a user touches touch screen 32 (or other controls associatedwith the user interface).

Wake circuit 62 also receives logical input line 86 c. Logical inputline 86 c is set to a logic HIGH value whenever power supply 76 ispresent. That is, whenever patient support apparatus 20 is plugged intoan A/C mains outlet, logical input line 86 c is set to HIGH. Thisensures that sleep components 78 will never be put into the sleep statewhen patient support apparatus 20 is plugged into a functioning A/C walloutlet. Stated alternatively, control system 54 only puts sleepcomponents 78 into the sleep state when it is functioning on batterypower (and when no activity is detected at touch screen 32 for thethreshold amount of time).

In summary, wake circuit 62 closes switch 84 whenever any of inputs 86a, b, or c has a logic HIGH value. The closing of switch 84 suppliespower to main controller 58 and H-bridge 68 via power line 90. Theremaining components with the set of sleep components 78 also receivetheir power via power line 90, although these connections are notillustrated in FIG. 3 .

Deep discharge circuit 60, as noted previously, shuts down electricalpower to all components of patient support apparatus 20 whenever thecharge state of battery 74 falls below a voltage threshold. Deepdischarge circuit 60 receives power from a power bus 92 that isoperatively coupled to battery 74 and power supply 76. Deep dischargecircuit 60 compares the voltage on power bus 92 to a threshold voltagelevel. If the voltage on power bus 92 is greater than the thresholdvoltage, then deep discharge circuit 60 supplies power to sleep powersupply 64 via an electrical connection 94. Deep discharge circuit 60supplies this power to sleep power supply 64 regardless of the sleep orawake state of sleep components 78. That is, power supply 64 suppliespower to touch sensors 80 and wake circuit 62 via power line 95 whensleep components 78 are in the sleep state, and also when sleepcomponents 78 are in the awake state. As a result of supplying power totouch sensor(s) 80, touch sensors 80 are able to detect a user touchingtouch screen 32 even when sleep components 78 are in the sleep state.Further, as a result of supplying power to wake circuit 62, wake circuit62 receives the necessary power to control switch 84, even when sleepcomponents 78 are in the sleep state.

When deep discharge circuit 60 detects that the voltage on power bus 92has fallen below the threshold voltage, it stops supplying electricalpower to sleep power supply 64. As a result of this power cut-off, wakecircuit 62 and touch sensors 80 do not receive any electrical power.Further, when wake circuit 62 does not receive any power, it stopssupplying a logical HIGH on its output 103 that is coupled to switch 84,thereby opening switch 84 and shutting off power to all of sleepcomponents 78. Consequently, when deep discharge circuit 60 detects thatpower bus 92 has dropped below a threshold voltage level, electricalpower is cut off to all of patient support apparatus 20. As noted,restoring power to patient support apparatus 20 is thereafter onlypossible by plugging the patient support apparatus 20 back into anelectrical wall outlet (i.e. providing power supply 76), or by replacingbattery 74 with a new battery that has a voltage above the thresholdvoltage used by deep discharge circuit 60.

One detailed manner of implementing deep discharge circuit 60, wakecircuit 62, and switch 84 is shown in FIG. 4 . As can be seen therein,wake circuit 62 includes a pair of Zener diodes 96, one of which iscoupled to input line 86 b and the other of which is coupled to inputline 86 c. The outputs from the two Zener diodes 96 are coupled togetherto create a first input line 98 to an OR gate 100. The coupling of theoutputs of the two Zener diodes together on line 98 has the effect ofperforming a logical OR operation on the inputs 86 b and 86 c. That is,if either of input lines 86 b or 86 c is logically HIGH, then line 98will also be logically HIGH; and only if neither of the input lines 86 band 86 c is logically HIGH will line 98 be logically LOW.

OR gate 100 also receives a second input 102 that is electricallycoupled to input 86 a. As a result, whenever input 86 a is logicallyHIGH, second input 102 will also be logically HIGH, and whenever input86 a is logically LOW, second input 102 will also be logically LOW. Theoutput 103 of OR gate 100 is fed to switch 84 and, as noted, closesswitch 84 when it is logically HIGH and opens switch 84 when it islogically LOW.

In the embodiment illustrated in FIG. 4 , switch 84 is comprised offirst and second Metal Oxide Semiconducting Field Effect Transistors(MOSFETs) 104 a and 104 b. When OR gate 100 outputs a logic HIGH signal,first and second MOSFETs 104 a and 104 b allow power from power bus 92to be supplied to power line 90 which, as discussed previously and shownin FIG. 3 , provides power to all of sleep components 78. When OR gate100 outputs a logic LOW signal, first and second MOSFETs 104 a and 104 bdo not allow power from power bus 92 to be supplied to power line 90,thereby cutting off power to sleep components 78 and putting them into asleep state.

Deep discharge circuit 60, which is shown to the right in FIG. 4 ,couples the power bus 92 input to a comparator 106 that compares avoltage supplied via power bus 92 to a threshold voltage. The thresholdvoltage is the voltage level that triggers a complete shutdown ofelectrical power to patient support apparatus. As noted, in someembodiments, the threshold voltage corresponds to approximately twentypercent of the voltage of battery 74 when it is fully charged. In otherembodiments, a different threshold voltage is used. Regardless of itsexact value, battery 74 provides the source of power for the thresholdvoltage. In this regard, it should be noted that the voltage compared tothe threshold voltage by comparator 106 is not the actual voltage ofpower bus 92, but rather is a reduced voltage that is reduced by thepresence of a resistor 105. Consequently, comparator 106 does notcompare power bus 92's voltage directly to a threshold, but insteadcompares a reduced voltage value that is linearly dependent upon thevoltage of power bus 92, to a threshold voltage.

The output of comparator 106 is fed into a control input 108 of a lowdrop fixed voltage regulator 110. Voltage regulator 110 is also coupledto power bus 92. So long as control input 108 receives a signal fromcomparator 106 indicative of the voltage level of power bus 92 beingabove the voltage threshold, voltage regulator 110 will output a fixedvoltage on output 112. Output 112 is coupled to sleep power supply 64and provides the electrical power to all of the electrical components ofpatient support apparatus that are not part of the set of sleepcomponents 78.

In some embodiments, main controller 58 is configured to output a logicHIGH signal on line 86 b based upon multiple factors. That is, inaddition to running a timer based off of a user touching sensor 80, asdiscussed above, main controller 58 is configured in at least oneembodiment to output a logic HIGH on line 86 b if a user has activatedexit detection system 72. By outputting a logic HIGH signal on line 86 bwhen the exit detection system 72 is activated, controller 58 preventspatient support apparatus 20 from entering the sleep state when exitdetection system 72 is armed. This outputting of a logic HIGH on line 86b occurs even if touch sensor 80 has not detected any touches for longerthan the threshold amount of time (as measured by the timer). In stillother embodiments, main controller 58 may be configured to take intoconsideration other factors when determining whether to output a logicHIGH or logic LOW signal on line 86 b.

Controller 58 is constructed of any electrical component, or group ofelectrical components, that are capable of carrying out the functionsdescribed herein. In many embodiments, controller 58 is a conventionalmicrocontroller, although not all such embodiments need include amicrocontroller. In general, controller 58 includes any one or moremicroprocessors, microcontrollers, field programmable gate arrays,systems on a chip, volatile or nonvolatile memory, discrete circuitry,and/or other hardware, software, or firmware that is capable of carryingout the functions described herein, as would be known to one of ordinaryskill in the art. Such components can be physically configured in anysuitable manner, such as by mounting them to one or more circuit boards,or arranging them in other manners, whether combined into a single unitor distributed across multiple units. The instructions followed bycontroller 58 in carrying out the functions described herein, as well asthe data necessary for carrying out these functions, are stored in amemory (not labeled) accessible to controller 58.

In some embodiments, touch screen 32 is constructed in one of themanners disclosed in commonly assigned U.S. patent application Ser. No.62/166,354, filed May 26, 2015, by inventors Daniel Brosnan et al. andentitled USER INTERFACES FOR PATIENT CARE DEVICES, the completedisclosure of which is incorporated herein by reference. The touchscreens disclosed in this application include dual sensing layers forsensing a users touch. In some embodiments, the dual layers include aresistive and a capacitive sensing layer. When such a dual sensing touchscreen is incorporated into control system 54 of the present disclosure,one of the sensing technologies—such as, but not limited to, thecapacitive sensing technology—may be included within sleep components78, while the other of the sensing technology is excluded from the sleepcomponents 78. In this manner, one of the sensing technologies stillreceives power while patient support apparatus 20 is asleep, therebyallowing patient support apparatus 20 to switch back to the awake stateupon a user touching touch screen 32 (as sensed by the non-asleepsensing technology).

As can be seen from FIGS. 3 and 4 , the electrical components used tochange patient support apparatus 20 from the sleep state to the wakestate are all hardware components. Main controller 58, which executessoftware, is one of the sleep components 78 and draws no power while inthe sleep state. As a result of this, patient support apparatus 20includes no instruction-executing components (e.g. microprocessors,microcontrollers, Systems-on-a-Chip (SoCs), etc.) that receiveelectrical power while in the sleep state. This helps reduce powerconsumption when patient support apparatus 20 is in the sleep state.Further, when touch sensors 80 are constructed as resistive sensors thateffectively act as an open switch when no one is touching them (such asdisclosed in the aforementioned patent application Ser. No. 62/166,354),patient support apparatus 20 consumes very little electrical power whilein the sleep state, thereby conserving the energy of battery 74.

Although FIG. 3 illustrates a single touch screen 32, it will beunderstood that this is merely for illustrative purposes. For example,when patient support apparatus 20 is implemented as a recliner, such asshown in FIG. 1 , it includes a first touch screen 32 positioned on afirst side of the backrest 24 and a second touch screen 32 positioned ona second and opposite side of the backrest 24. Both of these touchscreens 32 include touch sensors 80 that are powered by sleep powersupply 64, and both of these touch screen 32 include a display 82 (e.g.an LCD display or a static set of backlit icons) that is part of the setof sleep components 78. Further, in this configuration, when a usertouches either one of the touch screens 32 while patient supportapparatus 20 is in the sleep state, this awakens all of the sleepcomponents 78, including the display 82 of the other touch screen 32that was not touched.

Still further, when patient support apparatus 20 is implemented as arecliner (FIG. 1 ), it may include one or more patient control panelspositioned at locations that are convenient for the patient to use whileseated on seat 22. One such location is on one or both of armrests 26.When such patient control panels are incorporated into patient supportapparatus 20, they may be implemented as yet another touch screen 32, orthey may be implemented in other manners, such as one or more domeswitches. Regardless of their implementation, when a user touches thepatient control panel, this is detected by wake circuit 62 and wakes upthe patient support apparatus 20.

Still further, in some embodiments of patient support apparatus 20 thatinclude one or more patient control panels, patient support apparatus 20includes one or more lockout functions that can be activated by acaregiver from a caregiver control panel. When activated, these lockoutslock out one or more of the functions that are otherwise controllableusing the patient control panel. In some of these embodiments, controlsystem 54 is configured such that, if a patient touches a patientcontrol panel in an attempt to activate a locked out function, this willnot awaken patient support apparatus 20. In still other embodiments, thetouching of a patient control panel in an attempt to activate a lockedout function will awaken patient support apparatus 20, but will notresult in the function being performed.

FIG. 5 illustrates an alternative control system 54 a that may be usedwith any of the patient support apparatuses described herein. Controlsystem 54 a includes many of the components that are the same as controlsystem 54. Those components that are the same and that operate in thesame manner are given the same reference numbers and are not describedfurther herein. Those components that are different are given a newreference number and described in more detail below.

Control system 54 a differs from control system 54 in that it includes abattery monitor 114, a nurse call cable interface 116 adapted to coupleto a nurse call cable 118, and a propulsion system 120. Battery monitor114 is coupled to battery 74 and is adapted to take temperature,voltage, and current readings from battery 74. In at least oneembodiment, battery monitor 114 includes a battery fuel gauge marketedby Texas Instruments of Dallas, Texas, such as any one or more of thebq27400 and/or bq27600 series of fuel gauges sold by Texas Instruments.In other embodiments, battery monitor 114 includes one or morecomparable products manufactured by other semiconductor manufacturers.Regardless of the specific circuitry used, battery monitor 114 isconfigured to monitor a number parameters regarding battery 74, such as,but not limited to, its state of charge, remaining capacity, full chargecapacity, voltage, average current, temperature, current rate ofdischarge, time to empty at current rate of discharge, nominal availablecapacity, full available capacity, average time to empty, average timeto full, maximum load current, maximum load time to empty, availableenergy, available power, time to empty at constant power, internaltemperature, cycle count, state of health, charge voltage, chargecurrent, passed charge, and/or other parameters.

Battery monitor 114 reports various information it gathers from thestate of battery 74 to main controller 58. Main controller 58, in turn,displays some of this information on display 82. Main controller 58 alsotakes other actions in response to the battery information received frommonitor 114. One such action includes changing the state of one or morerelays 122 within nurse call cable interface 116. That is, controller 58opens or closes one of more of the relays 122 based upon information itreceives from monitor 114. Relays 122 are each in communication withnurse call cable 118. The opening or closing of relays 122 is thereforedetected by a nurse call system within a healthcare facility when theother end of nurse call cable 118 is plugged into a nurse call outlet.In most cases, nurse call cable 118 includes a separate wire for eachrelay so that the nurse call system is able to separately detect theopening and closing of each relay 122.

In at least one embodiment, monitor 114 sends battery information tomain controller 58 that is indicative that patient support apparatus 20is in need of a new battery. Main controller 58, in turn, opens orcloses one of relays 122. In this manner, the nurse call system isinformed via cable 118 that patient support apparatus is in need of anew battery. The particular relay 122 that is opened or closed inresponse to patient support apparatus 20 needing a new battery may varydepending upon the particular nurse call system that patient supportapparatus 20 is intended to be used with, as well as other factors. Inat least one embodiment, main controller 58 changes the state of a firstrelay 122 when exit detection system 72 detects a patient exitingpatient support apparatus 20, and changes the state of a second anddifferent relay 122 when it determines that a new battery is needed.

In still another embodiment, if exit detection system 72 is initiallyarmed while battery 74 is charged above a threshold, but then dropsbelow a threshold while exit detection system 72 is still armed,controller 58 is adapted to change the state of the same relay (firstrelay) that it changes when it detects a patient exiting patient supportapparatus. In this embodiment, the draining of a battery below thethreshold results in an alert signal being transmitted to caregiversthat is the same as if the patient had exited patient support apparatus20. This ensures that caregivers are notified before an impendingcomplete battery discharge, and allows them to take preventative action.

In still other embodiments, main controller 58 is adapted to change thestate of one or more relays based upon other information received frommonitor 114, and thereby inform the nurse call system of the state ofbattery 74. Such other information includes information indicatingwhether patient support apparatus 20 is in the sleep mode or the awakemode, information indicating that patient support apparatus 20 is aboutto enter the deep discharge prevention state and shut off its power viadeep discharge circuit 60, and/or information indicating that the chargelevel of battery 74 has fallen below a specific threshold.

In addition to, or in lieu of, sending battery information to a nursecall system via relays 122 and nurse call cable 118, main controller 58is also configured to provide improved and easily understood informationregarding the state of the battery to users via display 82. In at leastone embodiment, control system 54 a provides battery information to auser according to a battery monitoring algorithm 124 that is illustratedin more detail in FIG. 6 . As will be discussed in greater detail below,battery monitoring algorithm displays on display 82, or another display,battery status information that is selectable by a user and/or batterystatus information that is automatically determined by control system 54a based upon the state, history, and/or other factors of patient supportapparatus 20.

Battery monitoring algorithm 124 begins at step 126 where batterymonitor 114 reads the voltage, current, and temperature of battery 74.Battery monitor 114 then proceeds to step 128 where it updates thevarious parameters measured and recorded by monitor 114 utilizing thelatest voltage, current, and temperature readings taken at step 128. Atstep 130, monitor 114 exports various battery status data to maincontroller 58. The exported data may include a variety of differentparameters, such as, but not limited to, the battery's current capacity,remaining capacity, temperature, time left until discharge, any flags orwarnings regarding battery 74, and/or other battery status data.

The data exported from monitor 114 at step 130 is received by maincontroller 58 at steps 134 and 142. When main controller 58 receives thedata at step 134, it proceeds to display some or all of the receiveddata on display 82 at step 136. The data displayed by controller 58 atstep 136 is determined based upon a user's selection of what data todisplay that is made during a previous step 132. That is, at step 132, auser configures patient support apparatus 20 to display battery statusdata that is selected by the user. Control system 54 a may be configuredto allow a user to also display the selected battery status data indifferent manners, such as using different graphics. This selection isalso input into system 54 a at step 132. Step 132 is carried out, in atleast one embodiment, by via touch screen 32. That is, a user uses touchscreen 32 to select what battery data status he or she would likedisplayed, what format or graphics to use in displaying that data,and/or when to display that data. Once the user's selections are made atstep 132, main controller 58 records these selections and uses them todisplay the selected battery status data at step 136, as received and/orupdated at step 134.

Battery monitoring algorithm 124 is also configured to automaticallydisplay certain battery status data based upon the usage, state, and/orhistory of patient support apparatus 20. This automatic selection ofbattery status data to display is carried out in steps 138 through 144of algorithm 124. At step 138, main controller 58 determines how patientsupport apparatus 20 is being used. This determination includes any oneor more of a number of different aspects. In some embodiments, controlsystem 54 a determines when any motors or actuators of patient supportapparatus 20 are currently being used. In some embodiments, controlsystem 54 a specifically determines whether actuators that are used tolift a patient, such as those present on a cot for lifting a patientfrom a low height to a higher height, are being used. In thoseembodiments where patient support apparatus 20 includes an exitdetection system 72 and/or a propulsion system 120, controller 58determines whether these systems are in used at step 138. Controller 58may also determine whether still other systems, components, and/orfunctions are currently being used by patient support apparatus at step138.

After determining the current electrical usage state of patient supportapparatus 20 at step 138, controller 58 moves onto step 140 where itautomatically selects what battery status data to display, and whatformat to display the data in, based upon the determination made at step138. This step is discussed in more detail with respect to the variousexemplary graphics illustrated in FIGS. 7A through 9E. Once maincontroller 58 has selected the data to display and its format, itproceeds to receive the data to display at step 142 from monitor 114.Thereafter, it displays the selected and received data at step 144 ondisplay 82 and/or on one or more other displays.

FIGS. 7A-7C illustrate three different examples of graphics 146 a-c thatcontroller 58 may display on display 82, or another display, at step 136and/or step 144 of algorithm 124. It will be understood that graphics146 a-c, as well as graphics 146 d-n of FIGS. 8 and 9 , are merelyillustrative and non-exhaustive examples of the types of graphics thatcontroller 58 can display. Modifications to these graphics can be made,and controller 58 can be changed to display still other graphics thatare not shown in FIGS. 7-9 .

The specific illustrative graphics 146 a-c shown in FIGS. 7A-7C areparticularly suited for use with a patient support apparatus 20 that isadapted to lift a patient, such as, but not limited to, a cot. Cotstypically include one or more powered actuators that lift the patientfrom a low height to a high height. Often, the patient is first put onthe cot when the cot is at a low height and the cot is then lifted whileon the cot to a higher height. The cot is typically only transportedonce the patient has been lifted to the higher height. When controlsystem 54 a is implemented on a cot, or other patient support apparatus20 having a patient lifting function, control system 54 a displays oneor more of graphics 146 a-c on display 82. Graphics 146 a and 146 billustrate two different manners of displaying the number of lifts thatcan still be performed by patient support apparatus 20 based upon thecurrent state of battery 74. In some embodiments, this number iscalculated by dividing the remaining capacity of battery 74 by anaverage amount of energy consumed during one or more previous lifts. Inother embodiments, this number is calculated based upon otherinformation derived from battery monitor 114 regarding the current stateof battery 74.

Regardless of the precise manner in which the number of lifts ingraphics 146 a and 146 b is calculated, the presentation of this numberto the user of that particular patient support apparatus 20 provides theuser with information about the status of battery 74 in a manner that ismore useful than a simple indication of how far battery 74 has currentlydrained. That is, a user of that particular patient support apparatus 20may not have any idea of how much battery drainage results from one liftof a typical patient, and therefore may decide to recharge battery 74prior to its needing it, or may decide to continue to use battery 74longer than it is able to lift a patient. Indicating to the user anestimated number of lifts left therefore provides a far more useful andappropriate indication of the charge state of battery 74, particularlyfor cots and other patient support apparatuses 20 where the primarybattery drainage occurs due to patient lifting.

Graphic 146 c provides additional information about the state of battery74, and may be alternatively or additionally displayed on the display ofthe patient support apparatus 20 that displays graphics 146 a and 146 b.Graphic 146 c provides an indication about the health of battery 74,such as, but not limited to, when battery 74 may need to be replaced. Ascan be seen in FIG. 7C, graphic 146 c includes a plurality of bars 148that are selectively illuminated (or whose illumination color ischanged) based upon how healthy battery 74 is determined to be. When allof the bars are illuminated, or colored a first color, battery 74 is atis healthiest. As the health of battery 74 decreases, fewer and fewerbars 148 and/or portions of bars 148 are illuminated.

In some embodiments, the health of battery 74 that is displayed ongraphic 146 c is calculated based upon the current charge capacity ofbattery 74 versus the charge capacity of battery 74 when battery 74 wasinitially installed, or when battery 74 was new. In other words, in suchembodiments, graphic 146 c provides an indication of how much chargebattery 74 can retain when fully charged as compared to how much chargebattery 74 could retain when it was new. The greater the decrease in itscharge capacity, the lower the health indicated by graphic 146 c.

In other embodiments, graphic 146 c is based upon a number of timesbattery 74 has been discharged and recharged. In still otherembodiments, graphic 146 c is based upon how long battery 74 has beeninstalled patient support apparatus 20. In still other embodiments,graphic 146 c is based upon a combination of factors, such as thecurrent charge capacity of battery 74, the number of charge cycles ithas undergone, and/or the amount of time it has been installed. Otherfactors or formulas may also be used to calculate a health estimate ofbattery 74, which is then displayed on display 82. Regardless of themanner in which the health is specifically calculated, graphic 146 c isintended to convey information to a user about the overall health ofbattery 74 in an easily understood manner, and is not intended to conveyhow much charge remains on battery 74 for the current charge/dischargecycle. This latter information—how far battery 74 has currentlydischarged—may be displayed on display 82 in addition to the informationprovided by graphics 146 a, b, and/or c. Thus, in at least someembodiments, patient support apparatus 20 displays both a charge stateof battery 74 as well as its overall health. This gives the userinformation both about how much longer the battery will last until itneeds to be recharged, as well as information about how much longer thebattery will last until it needs to be replaced.

FIGS. 8A-8F illustrate examples of graphics 146 d-i that are suited foruse with a patient support apparatus 20 that does not have a primaryfunction of lifting a patient, or that includes substantially morefunctionality beyond lifting a patient. In other words, graphics 146 d-iare particularly suited for patient support apparatuses 20, such asbeds, stretchers and/or recliners, rather than cots. It will beunderstood, however, that graphics 146 d-i could be used on a cot, ifdesired. Controller 58 is adapted to display one or more of graphics 146d-i on display 82 when using algorithm 124, depending upon whether ornot a user has chosen to display one of graphics 146 d-i and/or whethercontrol system 54 a has determined that one or more of graphics 146 d-ishould be displayed based upon information determined at step 138.

Graphic 146 d is similar to graphic 146 c and provides a graphicalindication of the remaining useful life of battery 74 before it shouldbe, or needs to be, replaced. Graphic 146 e provides an indication ofthe current charge state of battery 74. In other words, it provides anindication of how charged battery 74 currently is. As shown in theexample of FIG. 8B, the indication is provided as a percentage. Graphic146 f similarly provides a percentage indication, but the percentageindication of graphic 146 f is indicative of the overall remaining lifeof the battery, not the remaining charge left in the battery for thisparticular charge cycle (as is the case for graphic 146 e).

Graphic 146 g provides an indication of the number of motion cycles thatcan still be carried out by patient support apparatus 20 given thecurrent charge state of battery 74. The precise definition of whatconstitutes a motion cycle will typically vary from patient supportapparatus to patient support apparatus. When patient support apparatus20 is implemented as a recliner, such as shown in FIG. 1 , a motioncycle may refer to the changing of the orientation of backrest 24, seat22, and leg rest 30 from one defined state to another, such as, forexample, moving these components from an orientation that defines aTrendelenburg position to a sitting position, or from a sitting positionto a stand-assist positioned, or from a flat position to a non-flatposition, or in still other ways. Similar definitions of motion cyclesmay also be used when patient support apparatus 20 is implemented as abed or stretcher. Still other definitions of motion cycles may also beused for beds, stretchers, cots, and/or recliners.

Graphic 146 h (FIG. 8E) provides an indication of the estimated amountof time that patient support apparatus 20 can continue to functionbefore battery 74 goes dead. Graphic 146 h may be generated based uponan averaging of the amount of energy drawn from battery 74 over someprior time period. Alternatively, graphic 146 h may be generated andupdated repeatedly based upon the current discharge rate of battery 74.As yet another alternative, graphic 146 h may be generated based upon acombination of one or more of these factors.

Graphic 146 i, like graphic 146 h, provides an indication of theestimated amount of time that patient support apparatus 20 can continueto function before battery 74 goes dead. Graphic 146 i, however,provides additional information about the state of battery 74. Thisadditional information includes a display of the historical rates atwhich energy has been drained from battery 74, as well as a display ofthe historical amounts of time left on battery 74 before it was drainedas determined according to the past drainage rates. More specifically,graphic 146 i includes a bar chart 150 and a current graph 152. Barchart 150 displays how long battery 74 has left for powering patientsupport apparatus. Bar chart 150 is arranged such that the rightmost barindicates the current amount of time that battery 74 has left forpowering patient support apparatus 20, while the bars to the leftindicate the past amounts of time that battery 74 had for poweringpatient support apparatus 20.

Graph 152 indicates the current drain rate of battery 74 at itsrightmost end, and previous drain rates of battery 74 to the left. Thus,as can be seen in FIG. 8F, patient support apparatus 20 is currentlydraining battery 74 at a higher rate than it was in an immediatelypreceding time period (the bar to the immediate left of the right-mostbar), and that, as a consequence, patient support apparatus 20 can onlybe expected to operate for another hour before battery 74 is drained. Incontrast, during the previous time period, battery 74 was drained at alower rate, and had battery 74 continued to be drained at that lowerrate, patient support apparatus 20 would have been expected to operatefor another three hours before being completely drained. Additional pastdrain rates and estimated times until complete drainage are alsoprovided in graphic 146 i.

FIGS. 9A-9E illustrate examples of graphics 146 j-n that are suited foruse with a patient support apparatus 20 that includes a self-propulsionsystem, such as propulsion system 120. Propulsion system 120 includesone or more motors that are adapted to drive one or more wheels onpatient support apparatus 20 so that a caregiver need only apply a smallamount of force when moving patient support apparatus 20 from onelocation to another. In at least one embodiment, propulsion system 120is constructed in any of the manners disclosed in commonly assigned U.S.Pat. No. 6,772,850 issued to Waters et al. on Jan. 21, 2000, andentitled POWER ASSISTED WHEELED CARRIAGE, the complete disclosure ofwhich is hereby incorporated herein by reference. Still other types ofpropulsion systems 120 may be used with the patient support apparatuses20 disclosed herein.

Controller 58 is adapted to display one or more of graphics 146 j-n ondisplay 82 when using algorithm 124, depending upon whether or not auser has chosen to display one of graphics 146 j-n and/or whethercontrol system 54 a has determined that one or more of graphics 146 j-nshould be displayed based upon information determined at step 138. Moreparticularly, in at least one embodiment, control system 54 a is adaptedto automatically display at least one of graphics 146 j-n wheneverpropulsion system 120 is activated. The display of these one or moregraphics 146 j-n occurs at a location on patient support apparatus 20adjacent to where the controls for propulsion system 120 are located sothat the user of the propulsion system can see these graphics whileoperating propulsion system 120.

Graphic 146 j provides an indication of how far patient supportapparatus 20 can travel via propulsion system 120 given the currentcharge state of battery 74. Graphic 146 k provides an indication of howmuch time the propulsion system 120 of patient support apparatus 20 cancontinue to operate before battery 74 is drained. The indicationprovided by graphic 146 k is based upon the current drainage rate ofbattery 74. Graphic 146 l provides an indication of an estimated amountof time that propulsion system 120 can continue to operate beforebattery 74 is drained. The time estimate provided in graphic 146 ldiffers from the time estimate provided in graphic 146 k in that theestimate for 146 l is based upon past drainage rates of battery 74 thathave been averaged over a certain amount of time, rather than theinstantaneous, or near instantaneous, drainage rate that is used tocalculate the time estimate in graphic 146 k.

Graphic 146 m includes a map 154 of a floorplan, or a portion of afloorplan, for the facility in which patient support apparatus 20 iscurrently located. Graphic 146 m further displays on the map 154 acurrent location 156 of patient support apparatus 20, as well as one ormore potential destinations 158. For each potential destination that isdisplayed, graphic 146 m indicates an estimated amount of chargeremaining on battery 74 should the user of patient support apparatus 20utilize propulsion system 120 to move patient support apparatus 20 tothat particular destination. This lets the user know which destinationsare within range of patient support apparatus 20 given the currentcharge state of battery 74. When graphic 146 m is used within a patientsupport apparatus 20, controller 58 includes map information within amemory on board patient support apparatus 20 that indicates distancesbetween locations within the facility it is located in. It furtherincludes data that is stored in memory that indicates the amount ofbattery drainage that is estimated to result from moving the patientsupport apparatus various distances. This latter data may bepreprogrammed, or it may be generated by patient support apparatus 20 byrecording drainage levels at the beginning and end of journeys that wereundertaken utilizing propulsion system 120.

In some embodiments, controller 58 gathers information about its currentlocation using one or more of the location determining methods disclosedin commonly assigned U.S. patent application Ser. No. 14/559,458 filedDec. 3, 2014 by inventors Michael Hayes et al. and entitled PATIENTSUPPORT APPARATUS COMMUNICATION SYSTEMS, or commonly assigned U.S.patent application Ser. No. 62/145,276 filed Apr. 9, 2015 by inventorsMichael Hayes et al. and entitled LOCATION DETECTION SYSTEMS ANDMETHODS; or commonly assigned U.S. Pat. No. 8,102,254 issued Jan. 25,2012 to inventors David Becker et al. and entitled LOCATION DETECTIONSYSTEM FOR PATIENT HANDLING DEVICE; the complete disclosures of whichare all hereby incorporated herein by reference. In still otherembodiments, other methods for determining the location of patientsupport apparatus 20 may be used.

In some alternative embodiments, graphic 146 m is modified to identify arange on map 154 that indicates how far patient support apparatus 20 cantravel via propulsion system 120, given its current charge state. Inthis alternative embodiment, graphic 146 m does not need to identifyindividual potential destinations 158, but instead can superimpose acircle (or other geographic shape) over map 154 that indicates theboundaries to which propulsion system 120 can drive patient supportapparatus 20 given its current charge state. Still further, in someembodiments, multiple circles (or other shapes) may be superimposed overmap 154 wherein each circle (or other shape) indicates how farpropulsion system 120 can drive patient support apparatus 20 untilbattery 74 reaches a specified level of discharge. Regardless of thenumber of circles or other shapes, controller 58 takes intoconsideration when constructing these shapes the locations of walls,hallways, and other obstacles or pathways (such as elevator locations)within the facility in which patient support apparatus 20 is located.Other variations for displaying map information and travel ranges arealso possible.

Graphic 146 n provides three different indicators regarding the currentstatus of battery 74: an efficiency indicator 160, a power indicator162, and a speed indicator 164. Efficiency indicator 160 provides anindication of how efficiently battery 74 is currently being used withrespect to propulsion system 120. That is, in at least one embodiment,efficiency indicator 160 indicates how much of the battery's capacitycan be delivered at the current discharge rate. In other embodiments,efficiency indicator 160 provides an indication of the distance thatpropulsion system 120 can propel patient support at the current drainagerate of battery 74.

Power indicator 162 provides an indication of how much power iscurrently being drawn from battery 74. Speed indicator 164 provides anindication of how fast patient support apparatus 20 is currently beingpropelled. All of the indicators 160, 162, and 164 are updated insubstantially real time while propulsion system 120 is operating,thereby giving the operator real time information about the efficiency,power, and speed at which propulsion system 120 is currently propellingpatient support apparatus 20.

Controller 58 is adapted, in at least one embodiment, to automaticallyselect at step 140 of algorithm 124 one or more of the differentgraphics 146 a-n described above and shown in FIGS. 7A-9E to bedisplayed on display 82, or elsewhere on patient support apparatus 20.As noted with respect to FIGS. 9A to 9E, controller 58 is adapted toautomatically select at least one of graphics 146 j-n wheneverpropulsion system 120 is activated. When propulsion system 120 is notactivated, controller 58 is adapted to select one or more of thegraphics shown in FIGS. 7A through 8F. In addition to those graphics 146that are automatically selected by controller 58, patient supportapparatus 20 may also display other graphics 146 that are selected by auser. The user is therefore provided with battery status informationthat is either chosen by the user, or that is automatically chosen bycontroller 58 in a manner that matches the chosen graphic to the currentstate of patient support apparatus 20 in a way that provides the userwith more useful manners of indicating the battery status. In sum,controller 58 displays some battery status information in a statesensitive manner that better aligns the graphic with the particularstate of patient support apparatus 20.

As mentioned, graphics 146 of FIGS. 7A through 9E are merelyillustrative examples of some of the types of graphics that may bedisplayed on patient support apparatus 20.

In still other embodiments, control system 54 a is adapted to operatewith a patient care device that is not a patient support apparatus 20.For example, in at least one embodiment, control system 54 a is adaptedto control a patient temperature management system, such as thosedisclosed in commonly assigned U.S. patent application Ser. No.14/282,383 filed May 20, 2014 by inventors Christopher J. Hopper et al.and entitled THERMAL CONTROL SYSTEM. When incorporated into such apatient temperature management system, control system 54 a is adapted todisplay at least one graphic that provides an indication of how muchlonger the patient temperature control unit can continue to providetemperature control given the current charge state of battery 74.

In still other embodiments, control system 54 a is modified to includeone or more power conservation features that limit the function ofpatient support apparatus 20 prior to battery 74 reaching its fullydrained state. In such embodiments, controller 58 is adapted to lock outcertain functions of patient support apparatus 20 based upon informationreceived from monitor 114. The locking out of these features occurs inaccordance with the logic set forth in the following chart.

Power State power supply battery charge > 1^(st) 2^(nd) threshold <battery charge < 76 present threshold battery charge < 1^(st) 2^(nd)threshold threshold Functionality full functionality full functionalitylimited functionality no functionality

As shown in the left-most column of the chart above, whenever patientsupport apparatus 20 is plugged into a functional A/C wall unit, orotherwise being powered by a non-battery power supply 76, controller 58provides full functionality of patient support apparatus 20 to a user.Similarly, as shown in the second column from the left above, wheneverpatient support apparatus 20 is operating on power supplied from battery74, but battery 74 has a charge level above a first threshold,controller 58 provides full functionality of patient support apparatus20 to a user. However, when the charge level of battery 74 falls belowthe first threshold, but remains above a second and lower threshold,controller 58 limits the functionality of patient support apparatus 20.Finally, as shown in the right-most column of the chart above, wheneverthe charge level of battery 74 drops below the second and lowerthreshold, all of the functionality of patient support apparatus 20 iscut off. In at least one embodiment, the second threshold is the same asthe threshold used by deep discharge circuit 60, and the termination ofall functions of patient support apparatus 20 is carried out by deepdischarge circuit 60.

Controller 58 is adapted, in several embodiments, to limit thefunctionality of the actuators used to move the various sections of thepatient support apparatus 20 (e.g. backrest 24, seat 22, and leg rest 30when patient support apparatus 20 is a recliner, or the various sectionsof deck 40 when patient support apparatus 20 is a bed or stretcher).More specifically, in at least one embodiment, when the charge level ofbattery 74 falls below the first threshold but remains above the secondthreshold, controller 58 is adapted to prevent the patient supportapparatus from moving to certain orientations and/or positions, butstill allow the recliner to move to certain other orientation and/orother positions. For example, in one embodiment, controller 58 preventsthe patient support apparatus 20 from moving to a Trendelenburg positionor a reverse Trendelenburg position when the battery charge level isbetween the first and second thresholds, but still allows the patientsupport apparatus 20 to move out of either of these positions, as wellas to move in other manners. In some embodiments, controller 58 also, oralternatively, prevents a user from raising the height of seat 22 ordeck 40 when the charge level of battery 74 is between the first andsecond thresholds, but still allows the user to lower the height of seat22 or deck 40 when the battery charge level is between the twothresholds. Controller 58 may also be adapted to prevent patient supportapparatus 20 from changing the configuration of its patient supportsurface (e.g. the deck of a bed or stretcher; and the backrest, legrest, and/or seat of a recliner) in any manner that is deemed to makeegress more difficult for the patient, while still allowing theconfiguration to be changed to any configuration that is deemed to makeegress easier for the patient.

By limiting the movement of patient support apparatus 20 when thebattery charge level drops below the first threshold, controller 58helps ensure that patient support apparatus 20 is not stuck in anunwanted configuration if battery 74 were to die. Such unwantedconfigurations are typically ones in which transferring the patient outof patient support apparatus 20 are difficult, more prone to falls, orboth (e.g. the Trendelenburg position, the reverse Trendelenburgposition, and/or any positions in which the seat area or patient supportsurface is not at its lowest height).

In some embodiments, controller 58 prevents exit detection system 72from being armed when the charge level of battery 74 falls below thefirst threshold. This helps prevent the patient monitoring functionprovided by the exit detection system 72 from prematurely terminatingdue to battery 74 going dead.

In at least some other embodiments, controller 58 may be configured toutilize more than two thresholds when determining what functions ofpatient support apparatus 20 to limit. That is, in some embodiments,patient support apparatus 20 is adapted to limit a first set offunctions when the battery drops below the first threshold, limit asecond set of functions when the battery drops below a second lowerthreshold, and cut off all functions when the battery charge level dropsbelow a third threshold that is even lower than the second threshold.When using three or more thresholds to limit the functions of patientsupport apparatus 20, controller 58 is configured in some embodiments tolimit the movement functions at higher thresholds than one or more otherfunctions that do not consume as much battery power as movement. Forexample, in at least one embodiment, controller 58 limits the movementof patient support apparatus 20 at a first threshold level while stillproviding the exit detection system 72 function, but turns off the exitdetection system 72 function when the voltage level of battery 74 dropsbelow a second and lower threshold. Only when the voltage level dropsbelow a third and lowest threshold are all functions cut off. In stillother embodiments, a first set of movement is cut off at a firstthreshold level and a second set of movement is cut off at a second andlower threshold voltage level. Still other variations are possible.

It will be understood by those skilled in the art that the functionalitylimiting carried out by controller 58 can be accomplished eitherseparately or in combination with the sleep/awake states discussedabove. That is, in some embodiments of patient support apparatus 20,control system 54 or 54 a is adapted to switch between the sleep andwake states, but does not reduce the functionality of patient supportapparatus 20 based upon the voltage level of battery 74 (other thancutting off all functionality at the threshold of deep discharge circuit60). In other embodiments of patient support apparatus 20, controlsystem 54 a is adapted to limit the functionality of various componentsin any of the manners described above based upon the charge level ofbattery 74, but does not switch between asleep and awake states. Instill other embodiments of patient support apparatus 20, control system54 a is adapted to both switch between asleep and awake states and limitthe functionality of patient support apparatus 20 when the charge levelof battery 74 falls below one or more thresholds.

Similarly, battery monitoring algorithm 124, discussed above, can beused alone in a patient support apparatus that does not include eitherthe function limiting feature or the asleep/awake states, or it may beused in a patient support apparatus 20 that also includes either or bothof the function limiting feature and the asleep/awake states.

Various additional alterations and changes beyond those alreadymentioned herein can be made to the above-described embodiments. Thisdisclosure is presented for illustrative purposes and should not beinterpreted as an exhaustive description of all embodiments or to limitthe scope of the claims to the specific elements illustrated ordescribed in connection with these embodiments. For example, and withoutlimitation, any individual element(s) of the described embodiments maybe replaced by alternative elements that provide substantially similarfunctionality or otherwise provide adequate operation. This includes,for example, presently known alternative elements, such as those thatmight be currently known to one skilled in the art, and alternativeelements that may be developed in the future, such as those that oneskilled in the art might, upon development, recognize as an alternative.Any reference to claim elements in the singular, for example, using thearticles “a,” “an,” “the” or “said,” is not to be construed as limitingthe element to the singular.

What is claimed is:
 1. A patient support apparatus comprising: a frame;a plurality of wheels; a support surface supported by the frame andadapted to support a patient thereon; a battery for powering a componentof the patient support apparatus, the battery being a rechargeablebattery; and a control system adapted to monitor a replacement status ofthe battery, to compare the replacement status of the battery to a firstthreshold and to a second threshold, to provide a first indication to auser that the battery should be replaced when the replacement status isbetween the first and second thresholds, to provide a second indicationto the user of a charge status of the battery, and to stop supplyingpower to the component when the replacement status is smaller than thefirst threshold.
 2. The patient support apparatus of claim 1 wherein thecontrol system is adapted to stop supplying power to the component whenthe replacement status is smaller than the first threshold even if thebattery still includes sufficient charge to power an actuator.
 3. Thepatient support apparatus of claim 2 wherein the control system isadapted to take into account an age of the battery since installation inthe patient support apparatus when monitoring the replacement status ofthe battery.
 4. The patient support apparatus of claim 3 wherein thecontrol system is also adapted to take into account a cumulative numberof times the battery has been re-charged when monitoring the replacementstatus of the battery.
 5. The patient support apparatus of claim 3wherein the control system is also adapted to take into account a ratioof a current charge capacity of the battery compared to a previouscharge capacity of the battery when monitoring the replacement status ofthe battery.
 6. The patient support apparatus of claim 5 wherein theprevious charge capacity of the battery is determined substantially atthe time the battery is initially installed on the patient supportapparatus.
 7. The patient support apparatus of claim 1 wherein thecomponent is an actuator adapted to move at least a portion of thesupport surface.
 8. The patient support apparatus of claim 1 furthercomprising a second component, wherein the control system is furtheradapted to stop supplying power to the second component when thereplacement status is smaller than the first threshold and the secondcomponent is activated in a particular manner.
 9. The patient supportapparatus of claim 8 wherein the second component is an actuator formoving at least a portion of the support surface and the particularmanner refers to moving the actuator in a first direction, but not asecond direction opposite to the first direction.
 10. A patient supportapparatus comprising: a frame; a plurality of wheels; a support surfacesupported by the frame and adapted to support a patient thereon; anactuator for moving at least a portion of the support surface; a batteryfor powering the actuator; and a control system including amicrocontroller for controlling the actuator and a voltage monitor formonitoring a voltage level of the battery, the control system adapted toterminate power to the microcontroller if the voltage level of thebattery drops below a threshold and to allow power to flow to themicrocontroller if the voltage level of the battery is above thethreshold.
 11. The patient support apparatus of claim 10 furtherincluding a user interface, and wherein the control system is furtheradapted to terminate power to the user interface if the voltage level ofthe battery drops below the threshold.
 12. The patient support apparatusof claim 11 wherein the control system further includes a sleep circuitadapted to change the patient support apparatus from an awake state to asleep state if the control system detects inactivity for more than athreshold amount of time, the sleep state consuming less power than theawake state.
 13. The patient support apparatus of claim 12 wherein thecontrol system is adapted to terminate power to the microcontrollerwhile the patient support apparatus is in the sleep state, and supplypower to the microcontroller while the patient support apparatus is inthe awake state provided the voltage level of the battery exceeds thethreshold.
 14. The patient support apparatus of claim 12 furtherincluding circuitry adapted to awaken the patient support apparatus fromthe sleep state to the awake state, the circuitry being implementedcompletely in hardware and utilizing no software.
 15. The patientsupport apparatus of claim 12 wherein the control system is adapted tocontinue to provide power to the voltage monitor while in the sleepstate.
 16. The patient support apparatus of claim 15 wherein the controlsystem is adapted to terminate power to the microcontroller using onlyhardware and not software.
 17. The patient support apparatus of claim 10wherein the control system is adapted to shut off power to allelectrical components of the patient support apparatus when the voltagemonitor detects that the voltage level of the battery has fallen below asecond threshold lower than the threshold and the patient supportapparatus is not plugged into an electrical power outlet.
 18. Thepatient support apparatus of claim 17 wherein the control system isadapted to turn on power to at least some of the electrical componentsof the patient support apparatus only when the patient support apparatusreceives electrical power having a voltage greater than the threshold.19. The patient support apparatus of claim 10 wherein the control systemis adapted to continue to supply power to a wake circuit while thebattery is below the threshold but above a second threshold, the wakecircuit is adapted to resupply power to the microcontroller when thewake circuit is activated, the wake circuit is coupled to a userinterface, and the wake circuit is adapted to be activated when a usertouches the user interface.